Mens Rea

Mens Rea meaning in law

The concept of mens rea, which is Latin for “guilty mind,” allows the criminal justice system to distinguish someone who set out with the intention of committing a crime from someone who did not mean to commit a crime. Mens rea refers to what the accused individual was thinking, and what his intent was at the time the crime was committed. Intent may be anything from a general intention to do something illegal, to a premeditated objective to commit a particular crime. To explore this concept, consider the following mens rea definition.

Definition of Mens Rea


  1. A person’s knowledge that his conduct is criminal.
  2. A criminal intent.
  3. Wrongful purpose or guilty knowledge.


1860-1865   New Latin mens rea (guilty mind)

Mens Rea and the Law

The concept of mens rea was brought up in the writings of English jurist Edward Coke, who promoted the idea that an act itself does not make a person guilty of a crime, unless their mind is also guilty. This is a vital differentiation between an individual who accidentally does something that turns out to be a crime, and someone who set out in their mind to do something to harm another person or their property. In modern law, a person cannot generally be convicted of a crime unless it can be shown that he knowingly engaged in the illegal act.

This concept is commonly seen in incidents resulting in severe injury or death. For example, a pedestrian steps off the curb in front of driver William, who slams on his breaks in an attempt to stop, but ends up hitting and killing the pedestrian. Although William technically killed the pedestrian, he had no intent to cause harm, and therefore no “guilty mind.” This is considered an accident, not a criminal act.

If, on the other hand, William had been driving around looking for a man he was angry with, with the intent of getting revenge. The man steps off the curb in front of William, who speeds up, hitting and killing the man. In this case, William obviously had the intent to find and harm the man, making this a criminal act for which William may be charged for murder.

Carelessness vs. Criminal Intent

Acting with carelessness is referred to in the eyes of the law as “negligence.” A careless or negligent act that results in injury or damage to another results in civil liability, and is rarely charged as a criminal offense. For example, leaving a rake out on the sidewalk where someone steps on it and is injured may result in the property owner being sued for medical bills associated with the injury.

There is a point at which, however, careless acts rise to the level of criminal negligence. For example, Steve leaves his lawnmower running on the front lawn while he runs into the garage to get his rake. The neighbor’s child tries to push the lawnmower and is seriously injured. Although Steve had no criminal intent, it is easy to assume that an unattended running lawnmower could pose a danger to neighborhood children, so Steve may be charged with criminal negligence. This would expose him to criminal conviction as well as civil liability.

Intentional and Unintentional Behavior

Mens rea is all about intent and the individual’s frame of mind when a crime is committed. Unintentional criminal acts fall into two basic categories, “mistake in fact,” and “mistake in law.” A mistake in fact applies to a person whose act technically fits the definition of a crime, but the person is unaware of a critical factor necessary for intent. For example, if Helen gives her neighbor a zip lock bag full of white powder in exchange for money, fully believing she was selling baking soda, she is mistaken about a critical factor of the crime. Helen did not have the intent to sell a drug, but intended to sell baking soda.

A mistake in law refers to a person who acts not knowing that the act was a crime. For example, Grandma Joanne sees one of her outdoor cats behaving strangely. Because the area has a problem with rabies, Grandma goes into the house, comes back with her handgun, and puts the cat out of its misery. A neighbor who hears the single gun shot calls the police who come to investigate, and Grandma tells them what happened. Grandma is surprised to receive a citation, and a criminal charge of discharging a firearm within the city limits. She had no idea that her act of putting down a rabid animal was technically illegal. In this case, Joanne was not mistaken about what she was actually doing, but only about the fact that it was against the law. Unfortunately, the legal system embraces the idea that ignorance of the law is no excuse.

Motive vs. Intent

Motive may be used by the prosecution to prove that the accused intended to commit the crime, and intended to produce a particular outcome. Motive may not, however, be used as a defense to an illegal act. For example, Nick and Cindy break into a cosmetics testing laboratory, damaging equipment and setting animals loose. The pair are arrested and charged with a variety of criminal offenses. Even though their actions were politically motivated in ending cruelty in animal testing, they could not use this as a defense. Guilt will be determined based on the pair’s actions and intent. In this case, Nick and Cindy intended to break into the facility without permission, and intended to cause damage, both of which are illegal acts. The fact that they did it “for a good reason” cannot be considered in a court of law.

Strict Liability

Certain laws, referred to as “strict liability” laws, do not take into account mens rea at all. Essentially these laws consider that, regardless of the intent of the individual committing the act, the act itself is deserving of criminal penalties. Many of these laws apply situations involving minors, such as statutory rape, and selling alcohol to minors. Strict liability also applies to defectively manufactured products.

Related Legal Terms and Issues

  • Civil LiabilityResponsibility for payment of damages, or for other court-imposed penalties in a civil lawsuit.
  • Criminal Charge – A formal accusation by a prosecuting authority that an individual has committed a crime.
  • Motive – A person’s reason for doing something; the goal of a person’s actions.